Errors can occur while processing a set of document pages into finished mailpieces. Certain types of these errors can result in the finished mailpieces not containing the correct set of document pages. For example, an incorrectly assembled mailpiece may also contain the last page of the previous mailpiece or the system may incorrectly identify a completed mailpiece as the previous mailpiece. In such case, the previous mailpiece document collation would be missing the last page and would be incomplete. The incorrectly assembled mailpiece would contain the last page from the previous mailpiece document collation, as well as the first page and possibly the last page of the intended document collation. Both of these mailpieces would be defective because each lacks the intended document collation contents.
While the vast majority of these errors can be detected through normal material tracking in paper handling equipment, errors in the paper handling equipment tracking logic implementation or material movement may be undetected by the tracking sensors. In such cases, a mailpiece could be processed incorrectly, yet be identified by the paper handling equipment system as being correct.
There are methods of validating the correct assembly of finished mailpieces, each with its own limitations. These include weighing, scanning, and measuring the thickness of the finished piece. There are also methods of insuring that the correct addressee on a sealed envelope matches the address printed on the envelope by marking the document with the addressee name or designation so that it can be read through the closed-face envelope or other container.
Scanning the finished mailpiece does not work on closed-face envelopes and other packaging and also may not work on windowed envelopes if the material within the envelope is not positioned accurately within the window, or shifts after being positioned accurately.
Weighing of a mailpiece requires calibration and does detect a data shift between mailpieces if all or some mailpieces within the job contain the same number of input documents, that is, document collation pages and enclosures are the same in number or otherwise weigh the same.
Finally, thickness detection has similar limitations as weighing and also cannot work on high page count documents such as high-count, non-folded documents because the tolerance of the document thickness may exceed the thickness of a single sheet. Moreover, insuring that the addressee on the contents matches the printed address on the envelope or container does not insure that the proper complete contents are enclosed in the finished mailpiece.